Lung Volmes& Capacity

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Lung Volumes &Capacities


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Lung volumes & Capacities

Lung volumes and lung capacities refer tothe volume of air associated with differentphases of the respiratory cycle

Lung volumes are directly measured

Lung capacities are inferred from lungvolumes

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Objectives

Define the following: Four volumes

TV nIRV

ERV nRV

Define the following: Four capacities

IC nVC

FRC nTLC

Also Closing Capacity3


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Typical volume/time tracing

A capacity is the sum of two or more volumes. 4


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Measurement

- estimating the volume of gas inside thethorax

- most common methods :

1. Gas dilution tests.

2. Body plethysmography (Body Box).

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Gas dilution tests

Person breathes nitrogen or helium gasthrough a tube for a specified period oftime

The final dilution of the gas is used tocalculate the volume of air in the thorax

* Helium doesnt readily diffuse across the alveolarcapillary membrane

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Gas dilution tests

Disadvantages :

- It is sensitive to errors

- Leakage of gas

- Failure to measure the volume of gasin lung bullae : because helium maynot mix with all parts of the lung .

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Body Plethysmography


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Body Plethysmography

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The most accurate way

The patient sits inside a fully enclosed rigid box andbreath through mouthpiece connected through a shutter

to the internal volume of the box

The subject makes respiratory efforts against the closedshutter (like panting), causing their chest volume toexpand and decompressing the air in their lungs

while breathing in and out again into a mouthpiece. Thevolume of all gas within the thorax can be measured byChanges in pressure inside the box and allowdetermination of the lung volume.


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PFT II 10


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Using the data from the plethysmographyrequires use of Boyles Law.

P1 V1 = P2 V2

Where:P1 and V1 are initial pressure and volume.P2 and V2 are final pressure and volume.Note: Both measurements are made at a

constant temperature.


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By this technique we will be able to know

Residual volume (RV)

Tidal volume (TV)

Total Lung Capacity (TLC)

Expiratory reserve volume (ERV) Inspiratory Reserve Volume (IRV)

Inspiratory capacity (IC)

Functional residual capacity (FRC)

Vital Capacity (VC)


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An up deflection is inspiration. A down deflection is

expiration.13

Tidal volume (TV)It is the volume of air inspired or expired with each breathduring normal breathing


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Tidal volume

Normal : 400-700ml (7ml/kg)

Tv varies with the build & age of the individualand the depth of respiration

Decreased in severe RLD


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Minute volume (MV) = TV x RR

Measurement during A/N : Usingwright respirometer

The instrument records for one minute

MV can be measured directlyTV is calculated by dividing MV by RR

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IRV: From TV to TLC17

Inspiratory Reserve Volume (IRV)

It is the maximal volume of air inspired with effortin excess of tidal volume


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ERV: From TV to RV18

Expiratory reserve volume (ERV)It is the maximal volume of air exhaled from the restingend-expiratory level or volume expired by active expirationafter passive expiration.


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ERV

Decreased in RLD

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PFT II 20

Residual volume (RV)

It is the volume of air remaining in the lungs at theend of maximal expiration.


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RV

Normal 25% of TLC

Increased

1. Br.Asthma : airway narrowing with airtrapping

2. Emphysema : loss of elastic recoil

Decreased- pulmonary fibrosis :Increased elastic recoil

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Vi l C i


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VC= TLC RV or

VC= IRV+TV+ERV22

Vital Capacityvolume of gas measured on complete expirationafter complete inspiration without effort


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VC

Decreased

1.OLD

2. RLD

( VC < 15 ml/kg (and VT < 5ml/kg)

indicates likely need for mechanicalventilation

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IC= IRV+TV. 24

Inspiratory capacity (IC):

It is the maximal volume of air inspired from restingexpiratory level


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TLC = FVC + RV ORTLC = RV + ERV + TV + IRV

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Total Lung Capacity (TLC)

It is the total volume of air within the lung after maximum

inspiration. (the maximum volume of air that the lung can contain)


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TLC

Increased

1. Br.Asthma : airway narrowing with airtrapping

2. Emphysema : loss of elastic recoil Decreased

- pulmonary fibrosis :Increased elastic

recoil - muscle weakness, Obesity

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F ti l R id l C it (FRC)


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FRC = RV + ERV.27

Functional Residual Capacity (FRC)It is the volume of air remaining in the lungs at the end of resting

(normal) expiration.


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FRC

Increased (>120% of predicted)

decreased elastic recoil: Emphysema

air trapping: B.Asthma, bronchiolar

obstructionDecreased

intrinsic ILD

by upward movement of diaphragm(obesity, painful thoracic or abdominalwound)

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PFT II 29

Lung volumes & capacities


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Lung Volume in

Obstructive Lung Disease


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PFT II 31


Narrowing and closure of airways during expiration tends to lead togas trapping within the lungs and hyperinflation of the chest.

Air trapping increase in RV

Hyperinflation increases TLC

RV tends to have a greater percentage increase than TLC

RV/TLC ratio is therefore increased (nl 20-35%)

Gas trapping may occur withouthyperinflation:(increase in RV & normal TLC)


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PFT II 32

Gas trapping and airway

closure at low lung volumecause the patient to breath athigh lung volume so FRC(RV+ERV) increased

This will prevent airwayclosure and improveventilation-perfusionrelationship

It will reduce mechanicaladvantage of respiratorymuscles and increases thework of breathing


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RV increasedTLC Nl /increased

RV/TLC increases

FRC increasedVC decreased

*Air trapping :Normal TLC with

increase RV/TLC

*Hyperinflation: Increase in both

TLC and RV/TLCl/


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PFT II 34

Lung Volume in

Restrictive Lung Disease


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PFT II 35

Reduction in TLCis a cardinal feature

1. In Intrinsic RLD (Interstitial Lung Disease)

TLC will decrease

RV will decrease because of increased elastic recoil (stiffness) ofthe lung and loss of the alveoli.

Breathing take place at low FRC because of the increased effortneeded to expand the lung .

RV/TLC normal


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PFT II 36

2. In extrinsic RLD (chest wall disease :kyphoscoliosis orneuromuscular disease:ALS,MG)

TLC is reduced either because of mechanical limitation tochest wall expantion or because of respiratory muscleweakness

RV is Normal because Lung tissue and elastic recoil is normalSo RV/TLC ratio will be high

Breathing take place at low FRC because of the increasedeffort needed to expand the lung .


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Restrictive Lung Disease:

RLD Intrinsic &severe chest

wall dis (pleuraland skeletal)

TLC decreasedRV decreasedRV/TLC normalFRC decreasedVC decreased

Extrinsic RLDTLC decreasedRV normalRV/TLC HighVC decreasedFRC decreased

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PFT II 38

3. In combined obstructive and restrictivedisease(e,g.sarcoidosis ,COPD+IPF)

Obstructive pattern on spirometry and

Reduced lung volume

4. In equivocal spirometry result :

e,g.when FEV1,FVC at lower limit of normal

IfTLC or RV raised the diagnosis is obstructive

lung disease


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RLDExtrinsic

RLDInterinsic

ObstructiveLung dis.

FEV1

FVC

FEV1/FVC

RV

TLC

RV/TLC

VC

FRC


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Functional Residual Capacity

Volume of air that remains in the lungs at theend of normal expiration.

FRC = ERV + RV

Facilitates uninterrupted oxygenation and co2removal across the alveolo-capillary membranein-between breaths.

Normal value :

male 3330ml

female- 2300ml

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FRC

Increases : Asthma, c/c bronchitis, PEEP Decreases : induction of a/n, post-op

Other Factors : Posture, age, bodyhabitus, pregnancy

FRC & Anaesthesia :

1. Pre-oxygenation

2. Induction of a/n

3. post-operative period

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Pre-oxygenation

Essential to any sequence of difficultairway management under GA

Provides an O2 reservoir within the lung

and body tissue to tide over the apnoeicspell needed during intubation

FRC - Main reservoir; 30ml/kg


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Resting metabolic O2 requirement =250ml/mt

Normally in room air FRC = N2 + O2

volume of O2 = 500ml

So a patient breathing room air canwithstand apnoea for about 2minutes without desaturating

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Pre-oxygenation

Denitrogenation : spontaneously breathing100% O2 for 5 minutes via a tightly fittingface mask.

Urgent situation : 4 maximal capacity

breaths FRC =2100ml (70kg) = 2100 ml O2

Patient can withstand apnoea for upto 8

minutes without desaturating Obese adult will desaturate to less than

90% in less than 3mts.

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FRC during intraop period

FRC reduced during a/n & surgery

Reduced by 20% during a/n induced withthiopentone & maintained by inhalational agents& IV narcotics

Irrespective of whether breathing is spontaneousor controlled

Magnitude of reduction is predominantlydetermined by body habitus

In morbidly obese FRC can reduce by as much as50% following induction of a/n

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Mechanism of reduced FRC :

- loss of outward elastic recoil of the chest wall

- During expiration chest wall is drawn inwards to aa greater extent FRC

- Inspiratory muscle tone of the diaphragm, scmt,scalene & IC muscles is lost following induction

- Cephalad displacement of diaphragm& a decreasein cross-sect. area of thorax both contributereduced FRC

Consequences :

-atelectasis- early airway closure

- altered pulmonary mechanics

ASSOCIATED V/Q MISMATCH


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FRC during intraop period

Reduction in FRC assoc. with a/n canbe partially reversed with :

1. CPAP

2. PEEP

3. 30 Head up tilt

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FRC & POST-OP PERIOD

Reduced FRC is the causative factor forpost-op hypoxemia, atelectasis &pnumonia

Impact of adverse effects minimised by :

- active lung expansion manoevers

- good post-op analgesia

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CLOSING CAPACITY

The lung volume ( during expiration) atwhich the small airways begin to close andtherefore prevent any further expulsion of

gas from related alveoli.

Measured by single breath nitrogenwashout technique.


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CLOSING CAPACITY

Single breath N2 washout tech.

- breathing room air the subject

slowly expires to residual volume

- slowly takes a single breath of

oxygen to max. inhalation- Breath is held for a few seconds

- Then slowly & evenly exhaled.

During the last phase the instantaneous nitrogenconc. & volume of the expirate are recorded & acharacteristic curve is obtained.

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CLOSING CAPACITY


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CLOSING CAPACITY

4 PHASES :

I -Dead space gas

II -Mixed dead space &

alveolar gas

III-Mixed alveolar gas fromall alveoli

IV-Sudden rise in conc of

N2.

CC - VOLUME AT WHICH

PHASE IV BEGINSPFT II 51


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CLOSING CAPACITY

Relationship between CC & FRC :

- If CC rises above the FRC someairways will be closed during part or wholeof the normal range of ventilation.

- so the blood passing through the closedareas of lung will not be fully oxygenatedand the arterial O2 will fall

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CLOSING CAPACITY


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CLOSING CAPACITY

Factors increasing CC :

1. Age :CC progressively increases fromlate teens onwards

CC=FRC - in the 60s,

- in the 40s in supine subjects

2.Position : CC increases in supine & head low

3. smokers, obesity, rapid IV transfusions, c/cbronchitis, left ventricular failure, MI

4. Post-op period : imp. Cause of post-ophypoxemia

PEEP increases the FRC above CC therebyincreasing PaO2 53


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DEAD SPACE

A) Anatomical Dead Space (VD Anat)

B) Physiological Dead Space (VD Phys)

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Anatomical Dead Space (VD Anat)

Volume of the respiratory passagesextending from the nostrils down tothe respiratory bronchioles(not

including) No exchange of gas b/w blood & air

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VD Anat

Normal volume 150ml Varies with:

1) Age : old age- 200ml

2) sex : young women ~ 100ml

3) Jaw position :

depression of jaw with flexion of head-

dec. VD by 30ml

Protrusion of jaw with extensionof head inc. VD by 40ml

Pneumonectomy & tracheostomy dec VD

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Ph i l i l D d S (VD Ph )


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Physiological Dead Space (VD Phys)

Fraction of the TV which is not availablefor gaseous exchange

VD Phys = VD(Anat) + VD (Alveolar)

Alveolar Dead Space :

-wasted ventilationoccuring in zones of lungwith high V/Q ratio

If there is no blood flow to a particular zone (eg.in pulmonary embolism) then all the

ventilation to that zone is wasted.

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VD Phys

VD Phys increased in :1. Old age

2. In upright position

3. With large TV4. High RR

5. When inspiratory time is reduced to 0.5 secorless during controlled ventilation

6. Bronchial asthma & c/c bronchitis7. Pulmonary embolism

8. Controlled hypotension

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Normally :

VD(Anat) = VD(phys)=1/3rd TV

Relationship b/w VD(Anat) & VD(phys) isconstant across TV

VD/VT = 0.25- 0.4

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Apparatus Dead Space

Volume of gas contained in anyanaesthetic apparatus b/w the patient andthat point in the system whererebreathing of exaled co2 ceases to occur

E.g. expiratory valve in magill system;side arm in ayres T piece

May add as much as 125 ml of dead spaceto the patient

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Alveolar ventilation( VA)

Definition : that part of the MV whichtakes part in gas exchange

Normal : 2.0-2.6 l/min/m2

3.5-4.5 l/min in adults

Pulmonary factor controlling the excretionof co2

Directly related to TV, VD(phy) & RR

VA = (TV Vdphy) x RR62


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Alveolar ventilation( VA)

Clinical assessment : most importantfor a/n

Observation of reservoir bag, movt

of chest & abdomen, rate of resp. &measurm. Of MV

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Lung Volmes& Capacity